The present invention relates generally to a hydraulic suspension system for a vehicle cab, and, more particularly, to such a system in which the cab is pivoted on a vehicle frame to expose an engine during repair operations.
Disclosed in Japanese Utility Model Laid-Open No. 63-158481 (1988) is a pneumatic spring type suspension apparatus in which a levelling valve and a cutoff valve are connected in series between an air reservoir and pneumatic springs which support a vehicle cab. When the cab is tilted, the pneumatic springs are sealed by the cutoff valve. However, since the cutoff valve merely prevents flow between the air tank and the pneumatic springs, removal of a load from the rear pneumatic springs after the cab has been titled, causes the rear springs to move upwardly complicating return of the cab to its operating position.
A similar problem exists with prior hydraulic vehicle cab suspension systems. As shown in FIGS. 1 and 2, a bottom portion of a cab 3 is supported on a vehicle frame 25 at four corner positions by hydraulic suspension mechanisms 19LF to 19RR. When the cab 3 is pivoted forwardly about a tilt shaft 51 for maintenance and repair of an engine (not shown) disposed under the cab 3, the rear hydraulic suspension mechanisms 19RL and 19RR are released from the load of the cab 3. Consequently, an air chamber of an accumulator communicating with each piston of the hydraulic suspension mechanisms 19RL and 19RR is extended to lift an attached bed or seat increasing its height by an amount h. For this reason, when the cab 3 is being returned to its operating orientation, the positions of the receiving seats 55 of the rear hydraulic suspension mechanisms deviate from the locus of the engaging members of the cab 3 to thereby prevent smooth locking thereof.
The object of this invention, therefore, is to provide a hydraulic suspension system which can assure proper positioning of the receiving seats of rear hydraulic suspension mechanisms when a vehicle cab is being returned to an operating position and thereby facilitating smooth engagement thereof with the receiving seats.